This stuff happens. I'd get it sorted myself, no point having a broken bass sitting around, and you'll find a lot of suggestions as to what PUPs you might upgrade to either elsewhere in this forum or as this thread develops.
Frankly, if you've emailed the store four times and had no reply simply name them here, it might encourage them to do the right thing. Of course they may have gone bust or there might be another legit reason for non-response but I still think it's worth you posting. I wouldn't bother with a small claims action, more trouble than it's worth, life's too short.